Wave guide dielectric heating apparatus



Patented July 17, 1951 UNITED STATES TENT OFFICE WAVE GUIDE DIELECTRIC HEATING APPARATUS Continuation of application Serial No. 698,360, September 20, 1946. This application August 2'7, 1949, Serial No. 112,780

6 Claims. (Cl. 21947) This is a continuation of copending application, Ser. No. 698,360, filed September 20, 1946, now abandoned.

This invention relates to high-frequency apparatus, and more particularly to a process and ap 'paratus for heating strip material by means of higlvfrequency electromagnetic energy.

An object of this invention is to devise means for heating strip dielectric material, in continuous fashion, by high-frequency electromagnetic energy.

Another object is to devise a novel apparatus for drying printing inks.

The foregoing and other objects of the invention will be best understood from the following description of some exemplifications thereof, reference being had to the accompanying drawings,

wherein:

Fig. 1 is a perspective view of one form of heating means according to the invention;

Fig. 2 is a perspective view, with parts broken away, of another form of heating apparatus; and

Fig. 3 is a cross-section of the apparatus of Fig. 2 taken along line 3--3 of Fig. 2 and looking in the direction of the arrows.

Referring, now, to the drawings, and particularly to Fig. lthereof, an elongated thin-walled hollow metallic wave guide, which is preferably of rectangular cross-section and one cross-sectional dimension of which is substantially twice the other, is shown at l. Two relatively elongated but shallow rectangular slot or openings, only one of which can be seen at 2, are cut entirely through the central portions of the two opposite longer side walls of said guide, one slot being cut through each of the said two walls and the two slots or openings being of exactly the same dimensions and positioned directly opposite each other. A strip 3 of dielectric material to be heated, which for example may be paper to which printing ink has been applied, is passed in continuous .iashion through wave guide I by means of the slots aforesaid. The slots are of suliicient length to accommodate the width of strip 3.

A coaxial line 7, consisting of an inner conductor 4 supported coaxially in an outer hollow conductor 5- by dielectric spacing means such as B,

, has its outer conductor 5 attached to the central portion of one of the longer side walls of the guide I near one end of said guide, the coaxial line extending atright angles to said side wall. Inner conductor 4 projects through an opening 8 in said side wall into the interior of the guide I' for a substantial distance, for example, approximately three-fourths of the distance to the opposite side wall. The free end of coaxial line I is adapted to be connected to the output pipe or lead of a source of high-frequency electromagnetic energy, for example, a magnetron.

The end of inner conductor 4 projecting inside the guide, which may for convenience be termed the excitin rod, is spaced a distance of a quarter wavelength (in the guide) from the nearer end of said guide, and said guide may have an overall length such that reflections from the end of the guide remote from the source do not seriously interfere with the transmission of energy along said guide. When high-frequency continuous waves are supplied to guide I by means of line T, waves having a TEo,1 mode are set up in said guide. With such waves, the electric intensityfield lines extend, in directions parallel to the exciting rod, from the inner surface of one of the longer side walls of the rectangle to the inner surface of the opposite side wall of the rectangle, and are spaced closest to each other in the vicinity of the center of said side walls, that is, in the region of the slots or openings 2.

As a result, these lines extend in a direction parallel to the direction of movement of the material 3 through the wave guide I, and are most concentrated in the region of the guide through which the material passes.

Therefore, as the dielectric material 3 passes through the Wave guide 1, a maximum heating of said material by high-frequency electromagnetic energy is accomplished, due to dielectric losses in said material as the high-frequency electromagnetic waves set up in the guide pass through said material. Dielectric losses in material 3 cause energy to be absorbed thereby, said energy being converted to heat in said material. If the apparatus is to be used in conjunction with a printing press, a printing inl; with high dielectric losses should be selected and utilized, so that the ink and not the paper absorbs most of the high-frequency power; this results in the effective drying of the printing ink.

Figs. 2 and 3 show a modification of the drying apparatus shown in Fig. 1. Upper and lower metallic half-wave-guide structures 9 and IE) are pivotally mounted with respect to each other, as by means of a hinge structure ll. Upper halfwave-guide structure 9 has an outer configuration which resembles the cover portion of a rectangular box, including a continuous rectangular top wall 12 (shown partially broken away for purposes of illustration), elongated continuous side walls [3 and I4, and a pair of continuous opposite end walls, one of which is shown at l5 and the other of which is directly opposite to the end wall 15; the structure 9 is open at its bottom due to the absence of a bottom wall. The wall members of the box-cover structure 9 are relatively thin, so that said box-cover structure is relatively thinwalled.

A plurality of spaced parallel fins or partition members l23, preferably made integral with the wall members of structure 9' and also made relatively thin, are arranged within the confines of box-cover 9. said fins being elongated and extending at right angles to side walls l3 and i l, being integral with top wall l2 and having their lower edges lying in the same horizontal plane as the lower edges of the side walls I3-l4 and end wall l5 of structure 9. Fins -43 are spaced apart a distance from eachother, and the end fins are spaced a distance from the end walls of structure 9, whichis sub,- stantially equal to the height (or depth) of the side walls and end walls of structure 9. Fin I6, which is the one adjacent end wall i5, is integral with side wall l3 and extends toward, but ends short of, side wall l4,so that an appreciable space exists between the end of fin l6 and wall I4. Fin 11, adjacent fin it, is integral with side wall M and extends toward, but ends short of, side wall I3, leaving an appreciable space between the end of fin H and wall I3, this space being made equal to that between fin l6 and wall i4. Adjacent fins, throughout structure 9, are integral with opposite side walls, so that alternate fins or partition members are integral with the same side wall; each of the fins of structure 9 is integral withone of the side walls thereof andextends toward, but falls short of, the opposite side wall, to thereby leave an appreciable space between the end of each fin and the side wall toward which it extends.

The lower half-wave-guide structure It is similar tothe upper half-wave-guide structure 9 in all respects, except that structure l0, which in its outer configuration resembles the base portion of a rectangular box, has its open side at the top thereof rather than at the bottom; corresponding parts of the lower structure It are therefore denoted by priming the reference numerals used for the similar parts in the upper structure 9. Structures 9 and I0 are so arranged with respect to each other and to the hinge structure II that upper structure 9 can be pivoted relative to, lower structure In in the] manner of an ordinary pivotable waffle iron, from a position in which the plane of top Wall I2 makes a substantial angle with the plane, of wall 12, to the relative position shown in Figs. 2 and 3, in which the walls [2 and I2 are substantially parallel to each other. Hinge structure II is attached to structures 9 and 10 in such a manner that when walls l2 and I2 lie parallel to each other, there is a relatively small but appreciable gap 24 between the lower edges of the fins, end walls, and side walls of structure 9 and the upper edges of the fins, end walls, and side walls of structure I0; a suitable limiting means (not shown) is arranged to stop the downward pivotal movement of structure 9 when walls I2 and I2 lie parallel to each other, whereby gap 24 is maintained open when structures 9 and Ill are closed for heating purposes.

Since structures 9 and I0 are similar, when said structures are pivoted to lie parallel to each other, as in Figs. 2 and 3, all points in each individual portion of the upperstructure 9 are positioned directly abovethecorresponding points in each individual portion of the lower struc-- ture II].

All parts of structures 9 and ID are made thin, and each structure may be realily produced by casting. The overall height of the device of Figs. 2 and 3 is preferably made approximately twice the distance between adjacent fins or partition members. When structures 9 and ID are in the position shown in Figs. 2 and 3, each pair of the upper and lower corresponding fins, such as I8 and 18', matches to form a side wall of a wave guide, so that each adjacent pair of such side walls, together with the portion of walls l2 and I! included between said pair of side walls, form 5 a separate wave guide for high-frequency electromagnetic energy, as do the first and last such side walls together with their respective adjacent outer end walls of the structures 9 and 10; therefore, a plurality of closely adjacent and parallel elongated wave guides are efi'ectively formed, and, since the wave guides arev in. communication with each other, due to the adjacent but oppositely-disposed spaces between the fins and the respective side walls of the structures, the effect is the same as if a continuous elongated wave guide had been bent or folded back and forth upon itself in the manner of an accordion. Since a continuous wave guide isthus in effect formed, high-frequency electromage netic energy supplied to the device ofjFigs. 2 and 3, at one end thereof, will flow in serpentine fashion down the device, toward the other'end; for example, it will flow from the inner, section of sidewalls l3-l3 and. end walls l5.l.5 toward side wall [4, down the waveguide prothence into and down thewaveguide provided between fins I'll 1' and l8--l8' toward: side walls I l-I4 and so on to thelast guide, providedpbetween thefinal closedendwall of the device and its adjacent pair of'flns 23-'23"which match to form a side Wall.

A thin plate 25 is attached to wall 15' of'the lower structure, near the intersection of walls l3 and it; this plate is of 'suflicient size toproject upwardly a substantial distance above the upper edge of wall it Attached to plate 25, and extending perpendicularly thereto, is a coaxial line i similarto the coaxial line of Fig. .1, the outer conductor E5 of line i being attachedfdie i rectly to the outer surface of said plate and the center of said outer conductor lying in theysame horizontal plane with the vertically-measured centerof gap 26. Inner conductord', ofjlinefl' extends, through an aperture in plate 25' and through a slot out in the lower edgeof wall I5and a slot cut in the upper edge of 'wall' l5, perpendicular to the plane of walls 15 and'i'fi, into the interior. of the wave guideformed between fins l9 and It, for a substantial distance. Conductor 4 is supported inhollow conductor "5"by means of dielectric spacers S. The freeend'of coaxial line I is, adapted tobe connectedjto the output pipe or lead of a source of high-frequency electromagnetic energy, for example, av magnet tron.

A strip of dielectric material 3, which mayas above be paper to which printing ink has been applied, moves, in a direction parallelto inner conductor 4, through the length of gap 'Mb'etween the contiguous surfaces of upper and lower structure 9 is returned to the position shown.

The end of inner conductor 4' projecting in- .side walls I5 and [5, which may for convenience be termed the exciting rod, is spaced a distance of a quarter wavelength (in the wave guide, members l5lli') from the side walls l3l3'.

When high-frequency continuous electromagnetic waves are supplied to the initial guide by means of line I, electromagnetic waves having a TEo,1 mode are set up in said guide.

above, from left to right in Fig. 2, in the manner described above, in the same mode. With such waves, the electric intensity field lines extend, in

, directions parallel to the exciting rod and there fore also to the direction of movement of the material 3, from the inner surface of one of the longer side walls of each rectangular guide to the inner surface of the opposite side wall of each, rectangular guide, and are spaced closest to each other in the vicinity of the center of said side walls, that is, in the region of the gap 24. Therefore, the field intensity lines extend in a direc- These, waves proceed down the effectively contiguous wave guide, in seprentine fashion as viewed from tion parallel to the direction of movement of the material through gap 24, and are most concentrated in the region of each guide (considering the upper and lower structures together as a plurality of guides, as described above) through which the strip dielectric material passes.

As the strip 3 passes through the wave guides of Figs. 2 and 3, a maximum heating of the strip dielectric material by high-frequency electromagnetic energy is accomplished, due to dielectric losses in said material as the high-frequency electromagnetic energy flowing through the guide passes through said material. As the strip 3 passes through gap M, it effectively and successively passes through each of the transverse wave guides, which are effectively in side-by side relationship, to the final guide. The high-frequency electromagnetic energy, as described above in connection with Fig. 1, is absorbed mainly by the printing ink on strip 3, due to its high dielectric losses, this absorption of energy resulting in the production of heat which efiectively dries said ink. Considered in another way, as the high-frequency electromagnetic energy flows in serpentine fashion down the device from left to right in Fig. 2, as described above, said energy is attenuated or absorbed by the strip dielectric material 3, said attenuation or absorption of energy serving to heat said strip.

It will be understood that the showing in Figs. 2 and 3 is merely for purposes of illustration, and that the relative dimensions of the contiguous or adjacent effectively parallel wave guides may be varied as desired, as well as the number of such wave guides which coact to form a single continuous wave guide.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. For example, a number of devices, each similar to that shown in Fig. 2, may be placed end-to-end if necessary or desirable, so that the strip 3 passes through each device in succession; in this case, each device would be fed from a separate source of high-frequency energy. Various other variations will suggest themselves. It is accordinglydesired that the *6 appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is: 1. Apparatus for heating strip dielectric mateterial, comprising upper and lower half-waveguide structures, at least a portion of the adjacent surfaces of said structures being spaced from each other so as to lie parallel to each other,

means .for passing strip dielectric material .through said space, and means for supplying high-frequency electromagnetic energy to said structures, each said structure including a plu rality of spaced planar partition members there- I rial, comprising upper and lower half-wave-guide structures mounted pivotally with respect to each other, at least a portion of the adjacent surfaces of said structures being spaced from each other when said structures are pivoted so as to lie parallel to each other, means for passing strip dielectric material through said space, and means for supplying high-frequency electromagnetic energy to said structures, each said structure including an open-sided metallic boxlike structure and a plurality of spaced planar metallic partition members therein, the planes of said members extending transversely to the direction of motion of said strip.

3. Apparatus for heating strip dielectric material, comprising upper and lower half-wave-guide structures mounted pivotally with respect to each other, at least a portion of the adjacent surfaces of said structures being spaced from each other when said structures are pivoted so as to lie parallel to each other, means for passing strip dielectric material through said space, and means for supplying high-frequency electromagnetic energy to said structures, each said structure including an open-sided metallic boxlike structure having two opposite side walls lying in planes parallel to the direction of motion of said strip, and a plurality of parallel spaced metallic partition members extending from one of said side walls toward the other of said side walls in planes substantially perpendicular to said side walls.

4. Apparatus for heating strip dielectric material, comprising upper and lower half-waveguide structures mounted pivotally with respect to each other, at least a portion of the adjacent surfaces of said structures being spaced from each other when said structures are pivoted so as to lie parallel to each other, means for passing strip dielectric material through said space, and means for supplying high-frequency electromagnetic energy to said structures, each said structure including an open-sided metallic boxlike structure having two opposite side walls lying in planes parallel to the direction of motion of said strip, and a plurality of parallel spaced metallic partition members extending from one of said side walls toward the other of said side walls in planes substantially perpendicular to said side walls, alternate members of said plurality extending from the same one of said side walls.

5. Apparatus for heating strip dielectric material, comprising upper and lower half-waveguide structures mounted pivotally with respect to each other, at least a portion of the adjacent surfaces of said structures being spaced from each other when said structures are pivoted so as to lie parallel to each other, means for passing strip dielectric material through said space,

and means for supplying high-frequency electromagnetic energy to said structures, each and structure including an open-sided metallic boxlike structure having two opposite side walls lying in planes parallel to the direction of motion of said strip, and a plurality of parallel spaced metallic partition members extending-from one of said side walls toward the other of said 'side walls in planes substantially perpendicular tosa'ld side walls, alternate members of said plurality extending from the same one of said side walls and all points in each individual member of said upper structure being positioned directly above the corresponding points in each 'indlvidualmemher of said lower structure "whensal'd-structures lie parallel't'o each other.

6. Apparatus for heating strip dielectrlcmaterial, comprising upper and lower half-waveguide structures mounted "pivctally "with respect to each other, at least a portion of "the adjacent surfaces of said structures being spaced tromeach other when said structures are pivoted so as to lie parallel to each other, means for passing-strip dielectric material'thr'ough said spa'ce,and means for supplying high-frequency electromagnetic energy to said structures, each said structure including an open-sided metallic boxllke structurehaving two opposite sidewalls'lyingfln planes parallel to the direction "of motion of said strip,

and a plurality of parallel spaced m'etalllc'jpartltion members extending from one 101' said side REFERENCES CITED The following references are of record/1n the fl1e of this patent:

'UNITED STATES PATENTS Number Name Date 2,226,871 Nicholas Dec. 31, 1940 2,283,935 King May 26,1942 2,433,842 Grifiin Jan. 6,1948 2,457,524 Bowen Dec. 28, 1948 2,457,695 Liskow Dec. 28, 1948 2,495,415 Marshall Jan. 24, 1950 2,495,429 Spencer Jan. 24, 1950 OTHER REFERENCES Electronic Heat, Steel, Nov. 12, ,1945,page.92. 

